Significantly, leukemic cells (both CML and AML) release Rab27a dependent 4-1BB containing endovesicles that upregulate STAT5 activity in Treg cells that leads to overexpression of effector/tumor Treg markers such as CD39, CCR4, TIGIT, TNFR2, CD30, and CCR8 via expression of Foxp3 [148]. Here, FOXP3 is linked to chronic myelogenous leukemia, BCR-ABL1 positive.